Maybe needs some nitrogen. That is what I think of when I hear/see yellow leaves.

maybe to much water?? also citrus is very shallow rooted so cultivating around the tree is a bad idea. The oak tree is a concern, since it will be major competition for soil and nutrients. but mulch is good for lots of reasons. I'd start with a good mulch and cut back the water especially in the winter months

If you are located in an area that may get late hard freeze you may want to hold off on the fertilizer and mulch another week or two. Organic is OK now in Houston, z9a/b. It takes a while to break down. Mulch holds heat in the ground makes trees freeae easier. Otherwise the above advice is good.

This year many think it will freeze again.

If your rootstock is trifoliate or one of its hybrids you may have high alkaline soil or water. This usually takes a little time to manifest itself, sort of like you describe.

If it is a mild case, try 3/4 lb. Magnesium sulfate. Start about a foot from the trunk and go out about five ft. This is an easy first treatment and it works in two ways. As a soil acidifier, and Mg ion is held in one of the coloring molecules in the leaves. If you have too much calcium, lime, magnesium deficiency usually follows. Iron too, but the soil can have a lot and it is not available to the tree.

If fertilizer, and Mg in the soil don't do the trick by late next month as it warms and the rootstock gets fully active, a foliar is needed. I'll get back on that.

Just make sure that the mulch is not right up to the trunk..

"I never put any fert around it anymore because of the light yellow color. I know citus trees like water too. Last year, I really didn't have to supplement due to the high amount of rain we received"

There is the culprit. That tree was use to getting good nutrition, and now you are seeing the signs of holding back, or poor root performance which still starves the tree..

Mike..:-)

Mike:

Depeding on the rootstock if there is an alkaline soil trees may not respond to fertilizer or iron treatments.

I've seen it build with time especially if the water has
a pH problem.

Your 100% right on that Tananman, that is why I have to use vinegar at almost each watering myself..Great point!

Mike..:-)